Sept. 24, 2005, 10:40PM
Dam damage forces evacuation on Trinity
By ALLAN TURNER and ZEKE MINAYA
Copyright 2005 Houston Chronicle
Trinity River Authority began releasing massive amounts of water from Lake Livingston northeast of Houston today in a frantic effort to lower the lake level after Hurricane Rita's winds and tropical waves dislodged part of the earthen dam's protective shield of boulders.
Riverside residents from Polk County to the Gulf of Mexico were evacuated from their homes because of flooding expected to occur in the river's flood plain. While river authority emergency management director Spencer Karr said the dam did not appear in immediate danger of failing, he said engineers thus far have not been able to determine the severity of the damage.
The release of 80,000 cubic feet of water per second, a process that should continue through Monday, will allow a thorough examination of the damaged structure, Karr said.
http://www.chron.com/cs/CDA/ssistory.mpl/chronicle/3368309
..the dam did not appear in immediate danger of failing, he said engineers thus far have not been able to determine the severity of the damage.
This is not very assuring.
http://www.pcoem.org/dam_failure.htm
"The dam is approximately 14,400 feet long and is generally between 45 and 60 feet high, reaching 90 feet at the old riverbed. The earth embankment has an impervious core and its section has slopes of 1 vertical to 2.5 horizontal. The crest of the dam is at elevation 145.0 ft. National Geodetic Vertical Data (NGVD), and is 24 feet wide. It accommodates a single-lane-paved road, which provides access to TRA personnel, law enforcement and emergency vehicles.
The dam is served by a concrete gravity spillway with an ogee crest at elevation 99.0 ft. NGVD. Releases are controlled by twelve 40-foot long by 32-foot high trainer gates. Concrete upstream and downstream aprons direct the water through the spillway and back to the original river channel.
The outlet works consist of a vertical inlet tower with five gates, a 550-foot long by 10-foot diameter conduit, a 170-foot long stilling basin, and a concrete broad-crested weir. A short channel downstream of the stilling basin directs flows back to the river.
Normal (conservation) pool level for the reservoir is 131.0 ft. NGVD, which encompasses a reservoir area of about 82,600 acres and storage of 1,750,000 acre-feet. Maximum pool design surcharge elevation is 134.0 ft. NGVD, which corresponds to a reservoir surface area of 88,900 acres and 2,045,000 acre-feet of storage. The drainage area above the reservoir is approximately 16,583 square miles and average flows are 7,440 CFS.
Livingston Dam is classified as a large, high-hazard structure with a recommended spillway design flood equal to the probable maximum flood (TDWR, 1978). According to the TDWR, the project will pass only 90% of the PMF before overtopping the dam."